How many mosquito nets are needed to maintain universal coverage: an update.

BACKGROUND: Insecticide-treated nets (ITNs) have served as the cornerstone of malaria vector control in sub-Saharan Africa for the past two decades. Over 2.5 billion ITNs have been delivered since 2004 primarily through periodic mass distribution campaigns scheduled at approximately three-year intervals, aligning with the expected lifespan of nets. Recent work indicates that ITN retention times are less than two years in most countries, raising key questions for quantification approaches and delivery frequency for ITN distribution. This paper models several quantification approaches for five typical ITN distribution strategies, estimates the proportion of the population with access to an ITN, and presents recommended quantification approaches to meet global targets for ITN access and use. METHODS: A stock and flow model with annual timesteps was used to model ITN distribution and resulting ITN access for 2020-2035 under five scenarios in 40 countries: (1) three-year mass campaigns, (2) full-scale annual continuous distribution, (3) three-year mass campaigns plus continuous distribution in the years between campaigns, (4) three-year mass campaigns at different quantification approaches, (5) two-year mass campaigns at different quantification approaches. All scenarios included ITN distribution to pregnant women at antenatal clinics and infants at immunization visits. RESULTS: The current status quo of conducting mass campaigns every three years using a population/1.8 quantifier is insufficient to achieve or maintain targets of 80% population access to ITNs in most malaria-endemic countries, given most estimated retention times are less than three years. Tailored three- or two-year mass campaigns were less efficient than annual continuous distribution strategies in nearly all settings. For countries with at least 2.5 year median ITN retention times, full scale continuous distribution provided better ITN access while needing 20-23% fewer ITNs compared to current mass campaigns. CONCLUSION: Given variation in ITN retention times across countries, tailored quantification approaches for mass campaigns and continuous distribution strategies are warranted. Continuous distribution strategies are likely to offer more efficient ways to maintain ITN coverage, with fewer nets, where ITN retention times are at least two and a half years. National malaria programmes and their funding partners should work to increase the number of ITNs available to those vulnerable to malaria, while at the same time working to extend the useful life of these critical commodities.

Prevention of Malaria in Pregnancy: What Do the Pregnant Women of Nigeria Know and Do about It?

Objective: We assessed knowledge, attitude, and practice regarding two malaria prevention measures (long-lasting impregnated mosquito nets, LLINs, and intermittent preventative therapy with sulphadoxine-pyrimethamine (IPTp-SP)) among pregnant women in Nigeria. Methods: Pregnant women selected from among the four communities of Nnewi were interviewed by using a semistructured, interviewer-administered questionnaire on the respondents' demography, knowledge of the cause, consequences, and malaria prevention methods. Also, a total of 48 focused group discussions, 24 key informant interviews, and 24 in-depth interviews were held among women leaders, village heads, pregnant women, community health workers, husbands of pregnant wives, and drug and insecticide-treated net sellers. Results: A total of 384 women (88.0% third trimester, 90.0% literate, and 41.1% primigravidae) participated. About 80.0% suffered from malaria during their current pregnancy. The majority was aware of the cause of malaria, local name of malaria, mode of transmission, risk of malaria among pregnant women, etc. However, their knowledge and attitude were inadequate regarding the symptomatology and complications of malaria in pregnancy, benefits of sleeping under the net or taking chemoprophylactic doses, or the concurrent use of both. About 80.0% had LLINs, yet only 41.5% slept under it the previous night. Only 31.0% had IPTp-SP doses under direct observation. Only 35.9% had a good understanding of IPTp-SP during pregnancy. Conclusion: Our work presents important practice gaps associated with the prevention of malaria during pregnancy. The pregnant women seemed to be aware of the basic concepts related to malaria but that does not translate into adequate attitude and practice necessary for malaria reduction.

The fabric of life: what if mosquito nets were durable and widely available but insecticide-free?

BACKGROUND: Bed nets are the commonest malaria prevention tool and arguably the most cost-effective. Their efficacy is because they prevent mosquito bites (a function of physical durability and integrity), and kill mosquitoes (a function of chemical content and mosquito susceptibility). This essay follows the story of bed nets, insecticides and malaria control, and asks whether the nets must always have insecticides. METHODS: Key attributes of untreated or pyrethroid-treated nets are examined alongside observations of their entomological and epidemiological impacts. Arguments for and against adding insecticides to nets are analysed in contexts of pyrethroid resistance, personal-versus-communal protection, outdoor-biting, need for local production and global health policies. FINDINGS: Widespread resistance in African malaria vectors has greatly weakened the historical mass mosquitocidal effects of insecticide-treated nets (ITNs), which previously contributed communal benefits to users and non-users. Yet ITNs still achieve substantial epidemiological impact, suggesting that physical integrity, consistent use and population-level coverage are increasingly more important than mosquitocidal properties. Pyrethroid-treatment remains desirable where vectors are sufficiently susceptible, but is no longer universally necessary and should be re-examined alongside other attributes, e.g. durability, coverage, acceptability and access. New ITNs with multiple actives or synergists could provide temporary relief in some settings, but their performance, higher costs, and drawn-out innovation timelines do not justify singular emphasis on insecticides. Similarly, sub-lethal insecticides may remain marginally-impactful by reducing survival of older mosquitoes and disrupting parasite development inside the mosquitoes, but such effects vanish under strong resistance. CONCLUSIONS: The public health value of nets is increasingly driven by bite prevention, and decreasingly by lethality to mosquitoes. For context-appropriate solutions, it is necessary to acknowledge and evaluate the potential and cost-effectiveness of durable untreated nets across different settings. Though ~ 90% of malaria burden occurs in Africa, most World Health Organization-prequalified nets are manufactured outside Africa, since many local manufacturers lack capacity to produce the recommended insecticidal nets at competitive scale and pricing. By relaxing conditions for insecticides on nets, it is conceivable that non-insecticidal but durable, and possibly bio-degradable nets, could be readily manufactured locally. This essay aims not to discredit ITNs, but to illustrate how singular focus on insecticides can hinder innovation and sustainability.

A survey of knowledge, attitudes and practices regarding malaria and bed nets on Bubaque Island, Guinea-Bissau.

BACKGROUND: Malaria remains a significant public health problem in Guinea-Bissau, West Africa. Government control measures include bed net distribution campaigns, however, local knowledge, attitudes and practices towards bed nets and malaria are uncharacterized on the remote Bijagos Archipelago. METHODS: Knowledge, attitude and practice questionnaires were conducted with household heads, aiming to explore the understanding of malaria and factors influencing bed net uptake and usage. Nets were observed in situ to appraise net quality and behaviour. All 14 villages and one semi-urban neighbourhood on Bubaque Island were included. One in 5 households containing school-aged children were randomly selected. RESULTS: Of 100 participants, 94 were aware of malaria and 66 of those considered it a significant or severe problem, primarily because of its impact on health and income. Transmission, symptoms and risk factors were well known, however, 28.0% of participants felt under-informed. Some 80.0% reported contact with distribution campaigns, with inter-village variability. Campaign contact was associated with feeling well informed (OR 3.44; P = 0.024) and inversely with perceiving malaria a household (OR 0.18; P = 0.002) or regional problem (OR 0.25; P = 0.018). Every household contained nets; every identifiable example was a long-lasting insecticide-treated net (LLIN), however, 23.0% of households contained at least one expired net. Replacements were in demand; 89.0% of households reported that all residents used nets, and average occupancy was 2.07 people per net; 65.2% stated that the repurposing of bed nets was common. Correctly using bed nets, defined by age, integrity and demonstration, was 35.0% and strongly associated with completing intermittent preventative treatment in pregnancy (RR 3.63; P = 0.014). CONCLUSIONS: Knowledge of malaria is good in these communities. Bed nets are used widely and are valued for their role in preventing malaria. However, their use is frequently sub-optimal and offers a target for improving malaria control by adapting popular distribution campaigns to provide more education alongside fresh LLINs. The impact of this could be significant as LLINs represent the mainstay of malaria prevention in Guinea-Bissau; however, the persistence of malaria despite the high uptake of LLINs seen in this study suggests that novel supplementary approaches must also be considered.

[Long-term travelers to malaria endemic areas†: What prevention strategies†?] / Séjours prolongés en zone endémique de malaria†: quelles stratégies de prévention†?

Long-term travelers are particularly exposed to malaria. It is essential to inform them about this risk, the recognition of the symptoms of the disease and the need for prompt treatment. Addressing any fears of travelers and answering their questions improve therapeutic adherence. Personal protective measures (repellents, mosquito nets) are fundamental and safe to reduce exposure to the vector of the disease. Depending on the individual risk of malaria and the special vulnerability of the traveler, short-term or prolonged chemoprophylaxis and/or emergency self-treatment and a rapid diagnostic test for malaria may be offered.

Les voyageur·euse·s de longue durée sont particulièrement exposé·e·s à la malaria. Il est essentiel de les informer sur ce risque, la reconnaissance des symptômes de la maladie et la nécessité d'un traitement rapide. Aborder les éventuelles craintes des voyageur·euse·s et répondre à leurs interrogations permet d'améliorer l'adhésion thérapeutique. Les mesures de protection personnelles (sprays répulsifs, moustiquaires) sont fondamentales et sûres pour diminuer l'exposition au vecteur de la maladie. Selon le risque individuel de malaria et les facteurs de vulnérabilité du·de la voyageur·euse, une chimioprophylaxie initiale ou prolongée et/ou un autotraitement d'urgence et un test de diagnostic rapide de la malaria peuvent être proposés.

Objective monitoring of mosquito bednet usage and the ethical challenge of privacy revelations about study bystanders: Ethical analysis.

Clinical trials and public health surveillance of bednet use for malaria prevention involve the ongoing collection of sensitive data from private settings. This article discusses risks to bystanders, who have not consented to participating in surveillance or research, but whose behavior may nevertheless be recorded. In the case of clinical trials, community consultation and consent processes are one well-accepted way to address potential risk to bystanders. I argue that the intrusive monitoring required by some bednet trials may render this type of consent insufficient. In these cases, either bystanders should be enrolled as participants and give consent or less intrusive monitoring methods should be used. Validated monitoring methods should also have relevance for practice beyond use in a clinical trial. Considering the global impact of malaria, applying these methods to public health surveillance would be a practical use. Existing justifications for surveillance without consent, which sometimes result in coercive public health measures, could apply to the case of bednets. Particularly in cases where there is the potential for harm to others, individuals who were not the original subjects of disease reporting are often caught in the surveillance net. Although an argument can be made that malaria meets this bar, considerations of feasibility, sustainability, and trust make intrusive surveillance unsustainable in the case of a daily, lifelong behavior such as bednet use.

Synergistic and antagonistic interactions between bednets and vaccines in the control of malaria.

It is extremely likely that the malaria vaccines currently in development will be used in conjunction with treated bednets and other forms of malaria control. The interaction of different intervention methods is at present poorly understood in a disease such as malaria where immunity is more complex than for other pathogens that have been successfully controlled by vaccination. Here we develop a general mathematical model of malaria transmission to examine the interaction between vaccination and bednets. Counterintuitively, we find that the frailty of malaria immunity will potentially cause both synergistic and antagonistic interactions between vaccination and the use of bednets. We explore the conditions that create these tensions, and outline strategies that minimize their detrimental impact. Our analysis specifically considers the three leading vaccine classes currently in development: preerythrocytic (PEV), blood stage (BSV), and transmission blocking (TBV). We find that the combination of BSV with treated bednets can lead to increased morbidity with no added value in terms of elimination; the interaction is clearly antagonistic. In contrast, there is strong synergy between PEV and treated bednets that may facilitate elimination, although transient stages are likely to increase morbidity. The combination of TBV with treated bednets is synergistic, lowering both morbidity and elimination thresholds. Our results suggest that vaccines will not provide a straightforward solution to malaria control, and that future programs need to consider the synergistic and antagonistic interactions between vaccines and treated bednets.

A systematic, realist review of zooprophylaxis for malaria control.

BACKGROUND: Integrated vector management (IVM) is recommended as a sustainable approach to malaria control. IVM consists of combining vector control methods based on scientific evidence to maximize efficacy and cost-effectiveness while minimizing negative impacts, such as insecticide resistance and environmental damage. Zooprophylaxis has been identified as a possible component of IVM as livestock may draw mosquitoes away from humans, decreasing human-vector contact and malaria transmission. It is possible, however, that livestock may actually draw mosquitoes to humans, increasing malaria transmission (zoopotentiation). The goal of this paper is to take a realist approach to a systematic review of peer-reviewed literature to understand the contexts under which zooprophylaxis or zoopotentiation occur. METHODS: Three electronic databases were searched using the keywords 'zooprophylaxis' and 'zoopotentiation', and forward and backward citation tracking employed, to identify relevant articles. Only empirical, peer-reviewed articles were included. Critical appraisal was applied to articles retained for full review. RESULTS: Twenty empirical studies met inclusion criteria after critical appraisal. A range of experimental and observational study designs were reported. Outcome measures included human malaria infection and mosquito feeding behaviour. Two key factors were consistently associated with zooprophylaxis and zoopotentiation: the characteristics of the local mosquito vector, and the location of livestock relative to human sleeping quarters. These associations were modified by the use of bed nets and socio-economic factors. DISCUSSION: This review suggests that malaria risk is reduced (zooprophylaxis) in areas where predominant mosquito species do not prefer human hosts, where livestock are kept at a distance from human sleeping quarters at night, and where mosquito nets or other protective measures are used. Zoopotentiation occurs where livestock are housed within or near human sleeping quarters at night and where mosquito species prefer human hosts. CONCLUSION: The evidence suggests that zooprophylaxis could be part of an effective strategy to reduce malaria transmission under specific ecological and geographical conditions. The current scientific evidence base is inconclusive on understanding the role of socio-economic factors, optimal distance between livestock and human sleeping quarters, and the effect of animal species and number on zooprophylaxis.

Meta-analysis of studies on chemical, physical and biological agents in the control of Aedes aegypti.

BACKGROUND: Aedes aegypti is a vector of international concern because it can transmit to humans three important arboviral diseases: yellow fever, dengue and chikungunya. Epidemics that are repeated year after year in a variety of urban centers indicate that there are control failures, allowing the vector to continue expanding. METHODS: To identify the most effective vector control strategies and the factors that contributed to the success or failure of each strategy, we carried out a systematic review with meta-analysis of articles published in 12 databases, from 1974 to the month of December 2013. We evaluated the association between the use of whatever chemical substance, mechanical agent, biological or integrated actions against A. aegypti and the control of the vector, as measured by 10 indicators. RESULTS: We found 2,791 articles, but after careful selection, only 26 studies remained for analysis related to control interventions implemented in 15 countries, with 5 biological, 5 chemical, 3 mechanical and 13 integrated strategies. The comparison among all of them, indicated that the control of A. aegypti is significantly associated with the type of strategy used, and that integrated interventions consist of the most effective method for controlling A. aegypti. CONCLUSIONS: The most effective control method was the integrated approach, considering the influence of eco-bio-social determinants in the virus-vector-man epidemiological chain, and community involvement, starting with community empowerment as active agents of vector control.

Long-term insecticidal activity and physical integrity of Olyset nets in Tafea Province, Vanuatu.

The long-term efficacy of long-lasting insecticidal nets (LLINs) depends on both the physical condition of the net and the residual activity of the insecticide. This study focused on monitoring these parameters in Olyset nets (Sumitomo Chemical Co., Osaka, Japan) (n = 101) that had been used for 1-3 yr in Tafea Province, Vanuatu. Net usage and frequency of washing was ascertained by questionnaire; the nets were assessed with regards to cleanliness and damage owing to holes. Insecticide efficacy was determined with cone bioassays using Anophelesfarauti Laveran. Net usage was high and 86.1% (87 of 101) of villages stated that they used the net every night. Washing of nets was low (11.9%, 12 of 101), and most nets (79.2%, 80 of 101) were considered dirty. Most nets were damaged (73.4% had holes), and 22.8% (23 of 101) had large holes (>200 cm2). The 24-h mortality of An. farauti exposed to nets aged 1-2 yr was 79.4%, while the mortality for nets 3 yr of age was significantly lower at 73.7%. There was no difference in the insecticidal activity of clean compared with dirty nets (mean 24-h mortality: Clean = 76.7%, Dirty = 77.1%). Although the majority of nets had holes, the physical condition of 8.9-22.8% of nets was altered so severely to potentially affect efficacy. Although the 3-yr-old nets would still be providing significant levels of insecticidal and personal protection, consideration should be given to replacing nets >3 yr old.

Strength of bed nets as function of denier, knitting pattern, texturizing and polymer.

BACKGROUND: Bursting strength is a standard method for evaluating mosquito net strength. This article suggests that tension strength with one grab and one hook better represent how holes are generated in bed nets in real life. METHODS: Measurements of bursting strength and tension strengths in the two directions are analysed for eight model nets created for the study. The nets were made in the most commonly used denier (75 and 100 D) and mesh (156 holes/inch(2)) for multifilament polyester yarns, texturized or not, and with 4 or 6 sided holes. All were made from one polyester quality. Data was arranged in a randomized, complete block design and analysed for significant variables and their interactions. Data was then subjected to regression analyses using net square metre weight as a weighting factor with stepwise removal of variables. This revealed how the four textile variables interacted and allowed for making predictions for the strength of commercial nets in polyester or polyethylene. RESULTS: For the model nets, higher denier provided higher bursting strength and tension strengths, texturizing weakened nets and four-sided holes were stronger than six-sided holes. Even when compensating for square metre weight, 100 D nets are stronger than 75 D nets. Results for the commercial polyester net nets are less clear, probably because of different qualities of polyester. Tensile strength: a 75 denier net knitted tightly to provide the same square metre weight as a standard 100 denier net therefore does not obtain the same strength. Polyethylene nets are made of mono-fibre yarns and, therefore, have higher tension strength in both directions than multifilament polyester nets. For bursting strength results overlap for 100 denier yarns of both yarn types. As a class, commercial polyethylene nets are stronger than commercial polyester net whatever method is used for evaluation. CONCLUSION: Tension strength measured in the length and width directions of the net using one hook and one clamp provide new relevant data as this method more closely imitates the cause of tear holes in nets as they occur in real life use. Using this methodology, the commercial monofilament yarn polyethylene nets are significantly stronger than the commercial multifilament polyester nets. This test method should be applied for nets used for years in the field.

Reported reasons for not using a mosquito net when one is available: a review of the published literature.

BACKGROUND: A review of the barriers to mosquito net use in malaria-endemic countries has yet to be presented in the published literature despite considerable research interest in this area. This paper partly addresses this gap by reviewing one component of the evidence base; namely, published research pertaining to self-reported reasons for not using a mosquito net among net 'owning' individuals. It was anticipated that the review findings would potentially inform an intervention or range of interventions best suited to promoting greater net use amongst this group. METHOD: Studies were sought via a search of the Medline database. The key inclusion criteria were: that study participants could be identified as owning a mosquito net or having a mosquito net available for use; that these participants on one or more occasions were identified or self-reported as not using the mosquito net; and that reasons for not using the mosquito net were reported. Studies meeting these criteria were included irrespective of mosquito net type. RESULTS: A total of 22 studies met the inclusion criteria. Discomfort, primarily due to heat, and perceived (low) mosquito density were the most widely identified reason for non-use. Social factors, such as sleeping elsewhere, or not sleeping at all, were also reported across studies as were technical factors related to mosquito net use (i.e. not being able to hang a mosquito net or finding it inconvenient to hang) and the temporary unavailability of a normally available mosquito net (primarily due to someone else using it). However, confidence in the reported findings was substantially undermined by a range of methodological limitations and a dearth of dedicated research investigation. CONCLUSIONS: The findings of this review should be considered highly tentative until such time as greater quantities of dedicated, well-designed and reported studies are available in the published literature. The current evidence-base is not sufficient in scope or quality to reliably inform mosquito net promoting interventions or campaigns targeted at individuals who own, but do not (reliably) use, mosquito nets.

[Ronald Ross, "doctor in spite of himself" and... Nobel Laureate in medicine]. / Ronald Ross, "médecin malgré lui" et... Prix Nobel de médecine.

After becoming a military doctor at the behest of his father, Ronald Ross was destined to make a discovery of paramout importance, i.e., malaria transmission through mosquito bites. This landmark discovery that was the fruit of a combination of curiosity, tenacity and luck, earned him the Nobel Prize in Medicine.